Scale-Dependent Browsing Patterns on Canada Yew (Taxus canadensis) by White-Tailed Deer (Odocoileus virginianus)

Canada yew (Taxus canadensis) is a clonal shrub that formsdiscrete patches and was formerly an important component of forest understories in muchof northeastern North America. Following Euro-American settlement, Canada yew has beenextirpated or reduced in abundance throughout much of its former range, particularly in the USA;winter browsing by white-tailed deer (Odocoileus virginianus) has been implicated as responsiblefor much of its decline. Little is known about the factors affecting deer browsing intensity onCanada yew. We examined factors related to browsing intensity on Canada yew acrossthree spatial scales in 29 forest stands in Michigan, USA. Browsing intensity on stems wasrelated principally to two factors acting simultaneously across multiple spatial scales. Browsing intensity was negatively related to amount of Canada yew at the scale ofthe forest stand and negatively related to distance from the edge of Canada yew patches,effectively creating refugia from browsing. The browsing patterns we observed suggest thatyew exists in two alternate stable states: (1) as loose aggregations of small stems or (2) large,dense patches of large stems. The implications of changes in deer density or snow cover to the probability of local persistence of Canada yew are discussed